1. Field of the Invention
The present invention relates to an electronic zooming circuit, which is suitable for utilizing in an apparatus such as a single-unit video camera-recorder.
2. Description of the Related Art
FIG. 3 shows an electronic zooming circuit of the prior art. In FIG. 3, CCD signals outputted from a solid state image sensing device 30, hereinafter called a CCD 30, are processed in a signal processor 31 with a predetermined signal processing method and a video signal of one field is wrote in a field memory 32. A readout address in response to a magnification of electronic zooming is assigned by such a device as a CPU (not shown) and each image signal for one line is read out in accordance with the readout address.
FIGS. 4(a) through 4(d) show that an image composed of n/2 lines in the middle of a picture composed of xe2x80x9cnxe2x80x9d lines is enlarged while the picture is doubled by a zooming process in horizontal and vertical directions. FIG. 4(a) shows an original video signal of one field written in the field memory 32. FIG. 4(b) shows a video signal of one field outputted from the field memory 32. The video signal is enlarged by 2 times in the vertical direction.
Since image signals of lines within a specific vertical range of a picture are repeatedly outputted twice from the field memory 32, when the double zooming process is performed in the vertical direction, vertical resolution of a picture outputted from the field memory 32 is deteriorated to one half of that of the picture written in the field memory 32.
Image signals outputted from the field memory 32 are written in a line memory 33, line by line. A readout address in accordance with a magnification of electric zooming is assigned by the CPU (not shown) and each image signal for one pixel is read out from the line memory 33 in accordance with the readout address.
Since image signals of pixels in a specific horizontal range of a picture are repeatedly outputted from the line memory 33 twice as shown in FIG. 4(c), horizontal resolution of a picture outputted from the line memory 33 is deteriorated to one half of that of the picture written in the line memory 33.
Accordingly, image signals obtained as mentioned above are sequentially processed with interpolation by an interpolation circuit 34 and a video signal of one field, which is processed with interpolation in horizontal and vertical directions, is produced as shown in FIG. 4(d).
In the electronic zooming circuit of the prior art as mentioned above, however, it is necessary for the electronic zooming circuit of the prior art to provide an expensive memory having a capacity of more than one field in the previous stage of the interpolation circuit 34. Accordingly, it is difficult to constitute a less expensive electronic zooming circuit.
Accordingly, in consideration of the above-mentioned problems of the prior art, an object of the present invention is to provide an electronic zooming circuit in a less expensive cost.
In order to achieve the above object, the present invention provides, according to an aspect thereof, an electronic zooming circuit obtaining an enlarged image from an original image in which one field is composed of N lines by enlarging only an area within predetermined horizontal and vertical ranges of the original image, the electronic zooming circuit comprising a solid state image sensing device of outputting a video signal of N lines in total within a period of one field by outputting an image signal of a predetermined line repeatedly during the period of one field, a memory of being written with image signals of a plurality of pixels including at least all pixels allocated within said predetermined horizontal range and being not written with an image signal of a same line repeatedly while writing said video signal of N lines outputted from the solid sate image sensing device, wherein only image signals of lines equivalent to the predetermined vertical range are repeatedly read out from the memory in accordance with a zooming magnification, a line memory of being written with an image signal of one line, wherein only an image signal of pixels equivalent to the predetermined horizontal range is repeatedly read out from the line memory in accordance with the zooming magnification and a interpolation circuit of obtaining the enlarged image by interpolating the video signal of N lines in the horizontal and vertical directions. The electronic zooming circuit is further characterized by that the solid state image sensing device repeatedly outputs only an image signal of lines equivalent to said predetermined vertical range within the period of one field when the zooming magnification is less than N/M times, where M and N are respectively a natural number and M is smaller than N, and inputs the image signal from the solid state image sensing device into the interpolation circuit after performing a zooming process in the line memory, and characterized by that the solid state image sensing device repeatedly outputs a video signal of M lines including at lest all lines in the predetermined vertical range within the period of one field when the zooming magnification is more than N/M times.
Furthermore, the electronic zooming circuit is characterized by that a value of the N/M is assigned to 2.
Other object and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.